1. Field of the Invention
The present invention relates to devices for transmitting and monitoring optical test signals through an optical fiber network. More particularly, the present invention relates to single devices that both transmit an optical test signal through a first optical fiber and receive that same test signal through a second optical fiber for analysis of the optical fibers through which the optical test signal travels.
2. Description of the Prior Art
There are many applications that utilize an optical fiber network to establish optical communications between a host digital terminal (HDT) at a central office and an optical network unit (ONU) at a remote location. Since a central office serves as the point of origin for the optical fibers in the optical fiber network, equipment is used at the central office to organize various optical fibers in the optical fiber network. In certain optical networks, the optical fibers at the central office are connected to dedicated pieces of equipment, such as optical signal transmitters, that serve only one purpose. If the optical fibers are to be connected to another piece of equipment, such as test equipment, the optical fibers must be manually connected to that new piece of equipment.
In more sophisticated applications, optical fibers are terminated at fiber administration systems at the central office. Fiber administration systems enable many different types of equipment to be connected to the optical fibers without having to reroute the optical fibers from their point of termination.
In many fiber administration systems, as the optical fibers in a network enter the central office, they are directed into an optical distribution frame where the individual optical fibers are terminated in an organized manner. Such fiber administration systems are exemplified by the LGX(copyright) fiber administration system which is currently manufactured by Lucent Technologies of Murray Hill, N.J., the assignee herein.
Each optical distribution frame located at the central office typically defines a plurality of bays, wherein each bay houses several different types of dedicated equipment shelves. One type of dedicated equipment shelf contained within a fiber distribution system is a fiber distribution shelf. Located within the fiber distribution shelves are optical connection ports that receive the ends of all of the individual optical fibers that enter the central office and are contained within the optical fiber network. By terminating each optical fiber at an optical connection port on one of the different fiber distribution shelves, the location of each optical fiber becomes known within the overall assembly. Once terminated at a known address on one of the fiber distribution shelves, each optical fiber can be selectively coupled to a variety of other types of equipment contained within other shelves of the fiber distribution system.
At the opposite end of the various optical fibers are the customers of the telecommunications provider. For customers having smaller scale telecommunications needs, the optical signals transmitted on the optical fiber network are converted to electrical signals, prior to termination of the customer premises in a traditional manner. As such, the entire optical network is controlled and maintained by the telecommunications provider. However, with customers that have large-scale telecommunication requirements, it is not uncommon for the telecommunications provider to run a pair of optical fibers from the optical network directly into the customer premises. One fiber is used to receive signals from the telecommunications provider and the other fiber is used to send signals to the telecommunications provider.
With customers that receive dedicated optical fiber pairs from their telecommunications provider, all incoming and outgoing transmissions are directed through these optical fibers. Accordingly, to disconnect either of these optical fibers is to completely disrupt the telecommunications service to that customer.
When a customer reports trouble with telecommunications transmissions, the problem can be either related to the optical fibers owned by the telecommunications provider or the telecommunications equipment owned by the customer. Since the optical fiber leading to the customer premises cannot be disconnected, it is difficult to pinpoint whether a problem is contained in the telecommunication provider""s equipment or the customer""s equipment. The result is that a technician from the telecommunications provider must be dispatched to the customer premises and time consuming manual tests must be conducted to locate the exact point of the problem.
In addition to monitoring and testing optical fibers leading to a specific customer premise, it may also be desirable to monitor and/or test newly deployed optical cables as well as other fiber optic cables routed between other locations in an optical fiber communications network.
The testing and monitoring of optical fibers also requires the deployment of a stable optical light source, i.e., a laser, which is typically embodied in a cumbersome piece of test equipment. Output levels of the laser are typically measured via a backface monitoring technique, as would be understood to persons skilled in the art. A drawback to tracking the output laser power using only the backface monitoring technique is that this technique does not always accurately reflect the laser power which has been output over the optical fiber. This may be due, for example, to temperature variations between the optical fiber and the laser apparatus which can cause slight misalignments to occur between the optical fiber and the laser, which is sometimes referred to as creeping.
A need therefore exists for equipment that can be used to test the integrity of an optical fiber pair leading to a specific customer premises from a remote location, thereby improving the efficiency by which a line error can be located.
The present invention is a module for use in an optical fiber administration system, or a dedicated system. The module contains both an optical transmitter and an optical monitor, wherein the module transmits a test signal over a fiber optic network and receives back that same signal through a different fiber in the fiber is optic network. By both sending and receiving the test signal, the integrity of different paths in the optical fiber network can be determined in a space efficient manner.
The module contains a microprocessor. The microprocessor reads data regarding the test signal as it is transmitted and that same test signal as it is received. This data may be read to an external shelf controller. The shelf controller utilizes the data from the microprocessor in the analysis of fiber optic loop conditions as well as the laser itself.